This invention relates to reduced volatility gelled liquid hydrocarbon treatment fluids and methods of their use and preparation.
Gelled liquid hydrocarbon fluids have been utilized in treating subterranean formations penetrated by well bores, e.g., for stimulation or sand control treatments such as fracturing or gravel packing, respectively. In fracturing treatments, a gelled liquid hydrocarbon fracturing fluid that may comprise particulates, often referred to as proppant, suspended therein is pumped through a well bore into a subterranean formation at a rate and pressure such that one or more fractures are formed or enhanced in a portion of the formation. Proppant particulates may be deposited in the fractures, inter alia, to prevent the formed fractures from closing, thereby maintaining conductive channels through which produced fluids can flow to the well bore. At a desired time, the viscosity of the gelled liquid hydrocarbon fluid may be reduced, or “broken,” and the fluid may be recovered.
Similarly, sand control operations, such as gravel packing, use gelled liquid hydrocarbon fluids, often referred to as gravel pack fluids. Gravel pack fluids usually are used to suspend gravel particulates for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation particulates, to form a gravel pack to enhance sand control. One common type of gravel packing operation involves placing a gravel pack screen in the well bore and packing the annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The gravel, inter alia, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the gravel pack fluid often is reduced to allow it to be recovered or produced back from the well bore.
Polyvalent metal salts of orthophosphoric acid esters have been utilized as gelling agents for forming high-viscosity gelled liquid hydrocarbon treatment fluids. Such gelled liquid hydrocarbon treatment fluids often have included particulate materials such as proppant or gravel, and oftentimes delayed breakers for causing the treatment fluids to break into relatively thin fluids so that the treatment fluids may be produced back. Descriptions of such high-viscosity gelled liquid hydrocarbon treatment fluids and methods of their use are set forth at least in part in U.S. Pat. No. 4,622,155 issued to Harris et al. on Nov. 11, 1986, and U.S. Pat. No. 5,846,915 issued to Smith et al. on Dec. 8, 1998.
While high-viscosity gelled liquid hydrocarbon treatment fluids and methods have been used successfully in some instances, problems in downstream processes have been encountered as a result of the use of certain phosphoric acid ester gelling agents. For example, plugging of refinery towers (which often process hydrocarbons produced from formations treated with gelled liquid hydrocarbon fracturing fluids) has caused many expensive, unplanned shut-downs of those towers. The plugging material is high in phosphorus and has been attributed to the phosphoric acid esters used as gelling agents in conventional reduced volatility gelled liquid hydrocarbon treatment fluids used during production of the hydrocarbons from a subterranean formation. The phosphoric acid esters are thought to contribute volatile phosphorus, which may condense on distillation tower trays, resulting in plugging of such trays, which may result in shut-downs of the towers. The volatile phosphorus also may carry over the tops of the distillation towers causing contamination of the hydrocarbon products produced. This volatile phosphorus problem has been attributed to the alleged inherent lack of stability of phosphate esters, which are believed to hydrolyze to form lower molecular weight compounds that are generally thought to cause the fouling problems. Despite these volatility and fouling problems, phosphoric acid ester gelling agents are desirable in that they are relatively low cost as compared to other hydrocarbon gelling agents. Thus, if a phosphoric acid ester gelling agent could be designed that did not have these associated volatility problems, this would be highly desirable.